Fixed problem with automatic responses to KEEPALIVE frames from server.

[spcmicro]

Fixed a problem with automatic responses to KEEPALIVE frames from server.

Reponses to the KEEPALIVE frames being sent from the server to the client were not being responded to. This caused a timeout of the connection on the server side after 30 seconds.

I modified the Validate method to return true when Header.Stream == 0. I think this is all that needs to be validated on a KEEPALIVE frame. The code was already present that sends the KEEPALIVE response to the server when Validate returns true.

NOTE: KEEPALIVE frames initiated by the client work fine. These changes only affect the client response to the server KEEPALIVE requests.

[maximdim]

@OlegDokuka any chance you can look at this? Thanks!

[spcmicro]

This was fixed by Eugene C. Closing PR.